Process and apparatus for supercritical water oxidation

ABSTRACT

An improved process and apparatus are disclosed for the supercritical water oxidation of organic waste materials which avoids or at least substantially reduces the corrosion and solids deposition problems associated with prior art techniques. According to this invention, externally heated supercritical water is fed to a platelet tube reactor to both protectively coat its inner surface and heat the waste stream to oxidation reaction conditions. Higher reaction temperatures can be used as compared to prior art processes, which significantly improves the reaction rate and permits smaller reactors to be used. The protective film of water on the reactor inner surface, coupled with the elimination of preheating of the waste material, substantially reduces solids deposition and corrosion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process and an apparatus for supercriticalwater oxidation and, in particular, to such a process and apparatususeful for the destruction of organic waste materials.

2. Description of the Prior Art

It is known that the fluid and solvating properties of water changedramatically at its thermodynamic "critical point"--i.e., at atemperature of about 706° F. and a pressure of about 3204 pounds persquare inch ("psi"). In particular, water above its critical point is asingle-phase fluid which is completely miscible with oxygen and mostorganic compounds. At supercritical water conditions, mass transferlimitations which limit the usefulness of oxidation processes insubcritical water are eliminated and the solubility of inorganic saltsdrops to the parts per million range. With the addition of oxygen,efficient destruction of organic compounds by oxidation is achieved,while inorganic substances can be separated and withdrawn for disposal.Specifically, organic compounds may be oxidized in supercritical waterto produce carbon dioxide and water. Following the oxidation, inorganicmaterials may be removed as dry solids or precipitated as salts andremoved as a brine. A significant advantage of such a process is theextremely short residence time required, on the order of 5-20 secondsdepending on process temperature, for destruction of organic compounds.

Supercritical water oxidation--defined as a process for oxidizingorganic waste compounds in supercritical water--has emerged as apotentially environmentally attractive technique for the safe andeffective treatment of toxic organic wastewaters and sludges. However,while organic compounds are completely miscible in supercritical water,inorganic salts present in the aqueous waste materials, or generatedduring the oxidation reaction, are essentially insoluble and may bedeposited as solids on reactor and other system surfaces, which may leadto plugging and low operating efficiencies. In addition to that solidsdeposition problem, corrosion of reactor and system surfaces has alsooccurred in supercritical water oxidation processes. Due to theseproblems, supercritical water oxidation has not been successfullycommercialized for the treatment of organic wastes and sludges.

Various attempts have been made to rectify these problems. For instance,U.S. Pat. No. 4,822,497 discloses a reactor designed so that thesupercritical temperature process stream is transferred to a cooler zonein the same vessel at high pressure to form a brine which facilitatesthe removal of solids. More recently, U.S. Pat. No. 5,252,224 disclosesa supercritical water oxidation process in which the reaction mixture ispassed through the reactor at a velocity sufficient to prevent settlingof a substantial portion of the solid particles from the reactionmixture.

There is still a need for a supercritical water oxidation process andsystem which avoids the above-mentioned significant problems of solidsdeposition and corrosion.

SUMMARY OF THE INVENTION

The present invention provides a process and apparatus for thesupercritical water oxidation of organic waste and other materials,which avoid the solids deposition and corrosion problems of the priorart. In particular, according to the present invention, organic wastematerial is oxidized in supercritical water in a tubular reactor whichcomprises an inner platelet tube, having a central reaction zone,supported within an outer shell. The waste material, along with asuitable oxidant, is fed to the central reaction zone under pressure andat variable temperature. Externally preheated supercritical water is fedto the annular space between the platelet tube and the shell where, dueto the pressure differential between the annular space and the reactionzone, it flows through the fluid passages provided in the wall of theplatelet tube and forms a thin, protective film on the inner surface ofthe platelet tube. This flow also serves to preheat the waste/oxidantstream in the reaction zone to a temperature which would initiateoxidation of the organics contained therein. Since the waste stream isnot preheated substantially before reaction, and further in view of theprotection afforded by the thin film of supercritical water on the innerplatelet tube surface of the reaction zone, solids deposition on, andcorrosion of, that surface is substantially eliminated. In addition,also because of the protection afforded by the thin film of water onthat surface, a higher reaction temperature may be employed, whichimproves the overall efficiency of the reaction and permits use of asmaller reactor. As a result, the required capital investment andoperating costs are lower than they would ordinarily be without theadvantages of the present invention.

The present invention also includes, in one embodiment, the use of asubmerged burner or combustor at the inlet of the platelet tube, atwhich a fuel is ignited to increase the temperature of the incomingwaste stream. The burner may be used together with injection into thereactor of clean, preheated, supercritical water to heat the wastestream to reaction temperature.

According to a further embodiment of the present invention, if no orless than the stoichiometric amount of oxygen is added to the reactor,by taking advantage of the dramatic difference in solubilities betweenorganics and inorganics in supercritical water the process may beoperated to separate organic from inorganic substances. Unreactedorganic substances may then be vented along with any gaseous reactionproducts and, if desired, subsequently oxidized in a gas turbinecombustor, a steam generator or other suitable devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a process and apparatus useful forsupercritical water oxidation according to the present invention.

FIG. 2 shows, in more detail, one embodiment of a reactor which may beused in the present invention.

FIGS. 3-8 show, in even more detail, several embodiments of platelettube-type reactors which may be used in the present invention.

FIG. 9 schematically illustrates a burner which may be employed in thepresent invention to heat a waste material to reaction temperature.

FIG. 10 illustrates another embodiment of the present invention in whicha platelet tube reactor and supercritical water conditions are employedto separate the organic and inorganic components of a waste stream,followed by oxidation of the separated organic components.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally, a supercritical water oxidation process comprises feeding anaqueous waste stream containing organic compounds, or a pumpable organicsludge, to a reactor along with an oxidant source and, optionally,supplemental fuel if the heat value of the waste is low. Followingoxidation of the organics in the reactor under conditions of temperatureand pressure above the critical point of water, solid/liquid andvapor/liquid separations are required.

FIG. 1 illustrates one embodiment of a process and apparatus of thepresent invention for the supercritical water oxidation of an organicwaste material. Although it is not the intention to be limited to thespecific arrangement shown in FIG. 1, for convenience the presentinvention will be explained and illustrated by reference to that figure.

As shown in FIG. 1, a waste material from source 10 at a high pressure(e.g., about 4000 psi) is fed via lines 13 and 16 to a tubular reactor17. The temperature of the waste is typically ambient (e.g., about 70°F.) but may be higher. Depending on the waste material, the temperatureshould be no more than about 650° F. High pressure has a beneficialeffect on the kinetics of the oxidation reaction in some cases.Accordingly, the minimum pressure is about 3500 psi, and it is preferredthat the pressure of the waste fed to the reactor is within the range offrom about 4000 psi to about 6000 psi.

Oxygen or other suitable oxidizing agent is also supplied to the reactor17 from source 11 via lines 14 and 16. Alternatively, or in addition,oxygen (or other oxidant) may be supplied to one or more points alongthe length of the reactor. For example, as shown in FIG. 1, oxygen maybe supplied to reactor 17 through lines 45 and 42. The place of oxidantaddition to the reactor depends on the properties of the particularwaste being treated. The addition of oxygen along the length of thereactor permits control of the reaction rate, and hence the temperaturerise, within the reactor.

In one embodiment of the present invention, useful when the intrinsicheat value of the waste material is low, a supplemental fuel from source12 is also fed to the reactor along with the pressurized stream of wastematerial and oxidant, via lines 15 and 16. Any convenient gaseous orliquid fuel may be employed (e.g., alcohol, methane, methanol, etc.).Ignition of the supplemental fuel in the reactor provides the additionalenergy necessary to sustain the oxidation reaction. Preferably, however,the temperature of the pressurized waste/oxidant stream is increasedfrom about ambient to reaction temperature by injection of water atsupercritical conditions into the waste stream at one or more stagesalong the tubular reactor.

Reactor 17 generally comprises a platelet tube concentrically supportedwithin a tubular shell. By "platelet tube" is meant a tube whose wall isformed of a plurality of stacked, thin plates having a large number ofprecisely engineered fluid passages formed therein to allow a fluid suchas water to pass through the wall from outside to inside, the number andshape of the interior openings of those fluid passages being designed toprovide a thin, protective film of water on substantially the entireinterior platelet tube surface.

Platelet tubes are known to be useful, for example, in cooling surfacesof aerospace vehicles. They are commercially available fromAerojet-General Corporation, Rancho Cordova, Calif.

Generally, platelet tubes may be designed to heat the waste stream toreaction temperature and provide protection to the inner reactorsurface. In order to heat the waste stream, the platelet wall fluidpassages may be designed to inject relatively large streams ofsupercritical water directly into the main body of the waste stream atappropriate points along the length of the reactor. In order to protectthe inner surface of the platelet tube from solids deposition andcorrosion, the platelet wall may also include a large number of smalleropenings for injecting supercritical water into the region along thatwall. The particular design of such smaller openings is not critical andmay be varied as long as an adequate protective thickness of clean,supercritical water is provided on substantially the entire innersurface of the platelet tube. For example, a "transpiration" typeplatelet tube may be employed, in which a large number of small openingsare provided in the plate forming the inner surface of the tube suchthat fluid is injected essentially in a direction perpendicular to thetube inner surface. The net result of this type of fluid injection isthat the injected fluid will mix with the main flow of waste andsimultaneously provide a thin film of clean supercritical fluid alongthe reactor wall.

Alternatively, and in a preferred embodiment, the small surface openingsare specially designed to inject the fluid in a direction substantiallyparallel to the interior tube surface, laying down on that surface athin protective film of supercritical fluid. In this embodiment, thatprotective film will be provided for a short length along the interiortube wall from each aperture, after which the fluid will tend to mixwith the main body of waste and increase its temperature. In anotherembodiment, both types of small openings (i.e., perpendicular andparallel injection) may be provided in the platelet tube inner surfaceto simultaneously heat the waste stream and protect the platelet tubeinner surface.

FIG. 3 schematically illustrates how the supercritical water may besupplied to the central passage of the platelet tube to both heat thewaste stream and form a protective film along the inner surface of theplatelet tube. As shown, waste is fed to and along the central passageof the platelet tube and supercritical water is fed to the annulusbetween the platelet tube and the shell. Fluid passages in the platelettube wall, and a pressure drop across that wall, permit supercriticalwater to flow from the annulus through the tube wall and then into thecentral passage of the tube. The direction and amount of flow ofsupercritical water into the central passage is controlled by the sizeand shape of the fluid passages in the tube wall. For example, in orderto heat the waste in the central passage, a number of generallyperpendicular streams (designated "A" in FIG. 3) may be provided,whereas a large number of generally parallel streams (designated "B" inFIG. 3) provide wall protection.

An example of a fluid flow pattern through the platelet tube wall thatefficiently covers its inside surface with a protective layer ofsupercritical water is illustrated in FIG. 4. That figure shows anexploded view of a portion of a platelet tube wall composed of sevendifferent plates 100 through 106. The pattern of flow in the illustratedembodiment is essentially hexagonal, with a single fluid inlet stream107 being dispersed into 1,134 flow paths at the opposite side of theplatelet wall. Specifically, a single fluid inlet stream 107 enters thetube wall through hole 108 in plate 100 and is immediately evenlydistributed by six channels in plate 101 to six outlets on the hexagonin plate 102 (only four of which, reference numerals 109 through 112,are shown in FIG. 4) as well as flowing straight through hole 113 inplate 102. The stream in each of those outlets is then split into sixother streams by hexagonal channels in plate 103, and a stream whichflows straight through. The process is repeated through plates 104, 105and 106 until the fluid finally exits the wall as 1,134 separate streamsschematically illustrated 114 in FIG. 4.

The shape of the apertures in plate 106 determines the direction of thefluid stream exiting those apertures into the central portion of theplatelet tube. For example, FIGS. 5 and 6 illustrate an embodiment whichcreates a flow of fluid in a direction generally parallel to the flow ofwaste and along inner surface 115 of the platelet tube. FIG. 5 (which isa plan view of a portion of the inside surface of the platelet tube)shows a plurality of apertures 116 in plate 106, each aperture beingdefined by a circular opening 117 partially overlaid by a trapezoidalopening 118. As shown best in FIG. 6 (which is a cross-section takenalong line 6--6 of FIG. 5), fluid flowing out through circular opening117 is deflected by surface 119 so as to flow along inside tube surface115. The apertures may be formed by any convenient technique, as isapparent to those of ordinary skill in the art.

FIG. 7 illustrates an alternative embodiment in which the many aperturesin the inner surface of the platelet tube are shaped such that the fluidstreams emanating from them are directed substantially perpendicular tothe inner surface of the tube, as shown schematically in FIG. 4.However, in addition to mixing with the main body of the waste stream toheat it, these many streams of clean, supercritical water also flowalong the interior wall of the platelet tube to form a thin protectivefilm.

FIG. 8 illustrates yet another embodiment in which a combination oftranspiration apertures 120 and wall protection apertures 116 areprovided in the inner surface of the platelet tube. With such a design,and by appropriate selection of the number and size of each type ofaperture, the degree of wall protection can be controlled along with theeffect on the temperature of the waste stream in the reactor by theinjected supercritical water.

Reactor 17 is shown in more detail in FIG. 2, where the same referencenumerals indicate the same elements as in FIG. 1. As illustrated in FIG.2, reactor 17 comprises a platelet tube 50 concentrically supportedwithin a tubular shell 51 and support members 52. The particularsupporting means employed is not important, and those skilled in the artcan select appropriate supports depending upon the specific size anddesign of the reactor. The platelet tube 50 defines a center tubularpassage 60 into which the waste/oxidant mixture is fed for reaction.Between the outer wall surface of platelet tube 50 and the inner wallsurface of shell 51 is provided an annular space 53 into whichsupercritical water is injected at one or more locations along thelength of the reaction zone. Because of the differential between therelatively high pressure of the injected supercritical water in annularspace 53 and the somewhat lower pressure of the waste stream in centerpassage 60, the supercritical water readily flows from the annular space53 through the fluid passages provided in the wall of the platelet tube50, into center passage 60. As noted above, the fluid passage aperturesprovided on the inner surface of platelet tube 50 are designed todisperse the injected supercritical water as a thin film along thatinner surface. As a result, the temperature of the waste/oxidant mixturein central passage 60 is increased while the thin film of water alongthe inner surface of platelet tube 50 protects that surface againstdeposition of solid material and corrosion. The thickness of theprotective film is not critical. It is only necessary that thesupercritical water be provided to the platelet tube so that a film isformed on the inner surface thereof so as to form a substantiallycontinuous isolating layer of pure fluid between the reactor wall andthe waste stream undergoing reaction.

The number and location of points along the reactor at whichsupercritical water is introduced into the annulus 53 are not criticaland depend on, for example, the temperature, flow rate and heat contentof the waste stream, the temperature and flow rate of the supercriticalwater, the size of the reactor, etc. Although four points of additionare shown in FIGS. 1 and 2, that is merely illustrative. A singleaddition may be sufficient. Those skilled in the art can determine theparticulars of how the supercritical water is injected into the annulus.Generally, the water injection along the length of the reactor is variedto allow temperature control within the reactor, provide an even flowdistribution of water along the length of the platelet tube, assuresubstantially complete coverage of the surface of the reaction zone by aprotective film of clean supercritical water, etc.

A substantial advantage of the present invention is the avoidance ofsolid deposition and corrosion on the reactor walls. This isaccomplished by providing the thin, protective film of water on theinterior surface of the reactor tube, as described above, and also byeliminating extensive preheating of the waste material prior toreaction, which can cause both solid deposition and corrosion. Instead,according to the present invention, the waste is heated to reactiontemperature by the injected supercritical water which may itself beheated outside the reactor by any suitable means. As shown in FIGS. 1and 2, for example, boiler-quality (i.e., clean) water from source 36 isfed via line 37 to heater 38, from which line 39 feeds heated water tothe reaction zone through lines 40, 41, 42 and 43. In an alternativeembodiment, pressurized colder water (e.g., about 4000 psi or higher andabout 300° F.) may be injected into the reaction zone at or near the endof the reactor to quench the reaction products. In FIGS. 1 and 2, thisembodiment is illustrated by stream 44.

The particular oxidant employed for the reaction is not critical, andgaseous oxygen is preferred. Other oxidants which may be employedinclude hydrogen peroxide, air, etc.

In general, the waste material to be treated according to the presentinvention may be any material containing organic and inorganiccompounds. Typically, the waste material is an aqueous wastewatercontaining organic compounds, and even toxic organics, such as sewagesludges, pyrotechnics, dyes, phenols, etc. Additionally, materials suchas municipal or industrial wastes, coal, etc., may be treated accordingto the present invention. The particular organic compounds which arecontained in the waste material, and their concentration, is ofimportance only in regard to the rate of reaction and the maximumtemperature achieved by the oxidation process. In other words, anyorganic compound in any concentration can be oxidized according to thepresent invention as long as the rate of reaction and maximumtemperature can be controlled. In addition, when the process of thepresent invention is operated in the absence of oxygen or with less thanthe stoichiometric amount of oxygen (e.g., to separate the organic andinorganic components of the waste stream, as described below), theconcentration of the waste material is less critical as long as theslurry or other form of waste material is pumpable or flowable.

In general, if necessary to provide pumpability or to reduce the heatcontent of the waste stream, water may be added. However, since additionof water, as well as the introduction of supercritical water to thereaction zone, increases the mass and volume of material flowing throughthe reaction zone, the size and hence the expense of the reactor mayincrease, as well as the expense of treating the liquid contained in thereaction products. It is therefore preferred that any pre-reactionaddition of water to the waste material be limited to that amountnecessary to make the waste flowable or pumpable and to prevent extremereaction excursions.

The residence time of the reactants in the reaction zone is dependant onseveral factors, including the temperature, the size of the reactor, theflow rates of materials into and through the reaction zone, etc. As ageneral rule, the present invention permits reaction temperatures to behigher than the temperatures of prior art supercritical water oxidationprocesses. In the past, the maximum temperature of reaction in suchprocesses was about 1100° F. due to the limitations of available reactormaterials. At temperatures higher than about 1200° F. and highpressures, containment design using conventional reactor materialscannot be used due to lack of strength, resulting in excessive thicknessas well as exposure to a corrosive environment. However, in the presentinvention, because the inner surface of the platelet tube reactor isprotected by a thin film of supercritical water and the pressurecontainment tube temperature is limited to that of the cleansupercritical water in the annulus, reaction temperatures higher than1200° F. may be employed. Typically, in the process of the presentinvention, the reaction temperature may vary from about 1100° F. toabout 1800° F., or higher, and is preferably about 1250° F. At thosetemperatures, the flow rates may be selected to provide a residence timein the reaction zone of about 5-20 seconds. In theory, the reactiontemperature may be increased even further as long as a sufficient amountof supercritical water can be fed through the platelet tube walls tokeep a protective film on its interior surface. The reaction temperaturemay be controlled by controlling the concentration of organics in thewaste stream which in effect regulates the heat of reaction per pound ofmaterial in the reactor. The use of high reaction temperatures in thepresent invention provides a significant advantage. In particular, asthe reaction temperature increases, the rate of the oxidation reactionincreases and the reactor size may be correspondingly decreased becausea shorter residence time is necessary. As a general rule, for everyincrease in reaction temperature of about 20°-30° F., the reaction rateapproximately doubles.

The size and wall thickness of the reactor are not critical and may bevaried to suit the particular requirements of any given situation. As ageneral rule, the size of the platelet tube will be determined by theamount of waste material being treated, its velocity and flow ratethrough the tube, the need to protect its inner surface with a thin filmof supercritical water, etc. The pressure tube (shell) of the system isdesigned in accordance with established codes such as ASME Section I orSection VIII. The reactor or platelet tube design is dictated by theflow requirements of clean water through the platelets to protect theinner wall of the platelet tube.

The mechanical design of the platelet tube takes into account thepressure drop across the platelet tube wall (generally less than 500psi) and the temperature which is controlled by the supercritical fluidflowing through the platelet tube wall (generally less than 1200° F.).The number of platelet holes or slots and their orientation is dictatedby the nature of and the quantity of the waste stream being processed.

The materials of construction of the platelet tube reactor used in thepresent invention are not critical, and those skilled in the art canselect appropriate materials of construction depending upon the wastebeing treated and the conditions of reaction. Typically, both theplatelet tube and the outer shell will be constructed of an alloy whichhas good high temperature properties, corrosion resistance, stresscorrosion crack resistance, etc. In fact, since the reactor shell is notin contact with the waste materials and typically is not exposed to thehigh temperatures existing in the central reaction zone, it is usuallysufficient simply to fabricate a shell according to the well-knownprinciples of high pressure vessels.

The size of the platelet tube reactor will vary depending principallyupon the amount and type of waste to be treated. For example, in orderto process 1.6 million pounds per hour of a liquid wastewater having aconcentration of sludge of 20% with a HHV of 5,000 BTU per pound, it isestimated that four reactors would be required, each having a diameterof approximately 4 feet and a height of about 15 feet.

At the end of the reaction zone, the material exiting the reactor, whichis a mixture of gaseous oxidation reaction products, insoluble inorganicmaterial, and steam, is usually still at supercritical water conditions.After removing (venting) the gaseous products, it is desirable to coolthe resulting gaseous/solid mixture to solubilize the solid inorganicmaterial and to facilitate separation and disposal of the solids. Thiscan be done using any convenient technique, such as dry physicalseparation (e.g., using a cyclone separator) or wet chemical separation.

A preferred method of cooling and separating the reaction productcomponents is illustrated in FIGS. 1 and 2. As shown in those figures,the reactor 17 discharges directly into a liquid/gas separator 18through inlet 55, and from which gaseous products are vented via stream30. The solid and liquid components of the reaction mixture are cooledin separator 18 to a temperature of about 200° F. by means of a cooledrecycle stream. It is desirable, and therefore preferred, to cool thereaction products as quickly as possible to re-solubilize the solidinorganics as a brine. This may be facilitated by supplying pressurizedcolder water at or near the end of the reactor, as described above, toquench the reaction products. The temperature of the quench water is notcritical and may be at any temperature below supercritical; for example,about 300° F. The resulting cooled liquid/solid mixture is removed fromseparator 18 through outlet 56 via stream 19, at which point it is splitinto two streams 20 and 25. Stream 25 may be chemically treated, ifdesired, to neutralize any acids present by addition of an appropriatechemical (e.g., sodium hydroxide, etc.) from source 29 through line 27.The resulting neutralized material preferably has a pH of about 7. Theresulting stream 28 is then cooled in heat exchanger 27 to a temperaturebelow the supercritical temperature and recycled to separator 18 vialine 29. It is preferred to tangentially introduce the recycle stream 29into separator 18 above a channel separator 59 to provide a wetted walland avoid salt accumulation.

Stream 20 can be cooled in heat exchanger 21 to facilitate disposal orfurther treatment.

Another possible alternative technique of separating the reactionproducts into their respective components is dry separation. Forexample, since the reaction product mixture is in vapor form, a cycloneseparator may be used to separate the high temperature reaction productsinto their solid and vapor components. The vapor components may then becooled, the water condensed out and the reaction products (such ascarbon dioxide) may be then vented to the atmosphere.

As mentioned above, one embodiment of the present invention involves theuse of a combustion device located at the reactor inlet to bring theincoming waste/oxidant stream up to reaction temperature. For example, asuitable combustor or burner may be located at the inlet of the platelettube reactor. A suitable fuel (e.g., alcohol, methane, methanol orsimilar liquid or gaseous fuel) and oxygen (or other oxidant) areseparately preheated externally of the reactor and fed to the burner atthe reactor entrance. Ignition of the fuel occurs at the burner face andincreases the temperature of the incoming waste stream. The type andamount of fuel, and the amount of oxygen, and their respective flowrates and temperatures may be varied to control the temperature increaseexperienced by the waste at the reactor inlet.

FIG. 9 schematically illustrates a burner located at the inlet of theplatelet tube. As shown in FIG. 9, the fuel and oxygen fed to the burner200 are mixed in the area of a cone-shaped diffuser 201, surrounded bythe waste stream. When the waste stream flows over the diffuser, a lowpressure center is created at the diffuser face which inducescirculation and mixing of the fuel and oxygen, thereby providing anefficient ignition and heating of the waste material. Liquid and gaseousfuels of any kind can be employed. Ignition of the fuel at the diffuserface of the burner is assured by preheating both the fuel and oxygenstreams, using any suitable technique.

The concept of preheating internally as described is also of particularinterest in those cases where the waste or hydrocarbon containing slurryis treated at supercritical water conditions to effect separation oforganic and inorganic materials. Oxidation of the separated organicmaterials may be performed outside of the reactor for purposes ofgenerating power, etc. The internal preheater in the case describedabove serves the purpose of bringing the stream to be treated to thecritical temperature and above to effect the separation desired. Forexample, FIG. 10 illustrates a platelet tube reactor system which may beemployed to separate organics from a waste stream under supercriticalconditions for subsequent oxidation. As shown in that figure, a wastematerial (such as a sewage sludge) is fed to platelet tube reactor 300via stream 301. If necessary to heat the sludge stream, oxygen and/orfuel may be fed via streams 303 and 302, respectively. The materialsexiting reactor 300 via stream 304 are at supercritical conditions andare fed to separator 305, where they are cooled and from which solidsare removed via stream 306. The hot, pressurized gases are removed fromseparator 305 via line 307 and are fed to an expander generator 308,where the pressure is reduced from, e.g., about 4000 psi to about 300psi. The temperature of the gases (and organics) in stream 307 istypically about 700° F.

The reduced pressure gases, at a temperature typically about 300° F.,are then fed via line 309 to combustor 310, along with fuel (via line311) if required to stabilize combustion of the organic substances. Airfor combustion is fed via line 314 to turbine generator 313 and then tocombustor 310 via line 315. The resulting gaseous oxidation reactionproducts, at a temperature of about 2300° F. and a pressure of about 230psi, exit combustor 310 via line 312 and are fed to turbine generator313, from which a reduced pressure gas stream is removed via line 316.Typically, gas stream 316 is at a temperature of about 1050° F. and apressure of about atmospheric. Of course, depending upon the processconditions selected, these temperature and pressure conditions may bedifferent.

Gas stream 316 is used to heat water stream 322 in a heat exchanger, asshown, to about 750° F, after which it is passed through a condenser.Harmless combustion gases are vented through line 317 and the condensedwater in stream 318 may be treated in apparatus 319 to provide potablewater exiting via line 320. Water stream 320 may be split into stream321, a source of potable water, and stream 322 for recycle to reactor300. As shown, water stream 322, after being pressurized to about 4000psi in pump 323 and heated to about 750° F., is fed to the annulus ofreactor 30 via lines 322a, 322b, 322c and 322d, although the number andlocation of such points of introduction may be varied as desired tomaintain supercritical conditions in reactor 300.

What is claimed is:
 1. A process for the supercritical water oxidationof an organic waste material comprising:(a) feeding a pressurizedaqueous mixture of said waste material and an oxidant source to a centerreaction zone of a platelet tube reactor which is supported within anouter shell and whose outer surface defines, together with an innersurface of said shell, an annular space, a wall of said platelet tubebeing provided with fluid passages which permit the flow of fluid fromsaid annular space into said center reaction zone through a plurality ofapertures; (b) igniting a fuel at an inlet of said reaction zone toincrease the temperature of said pressurized aqueous mixture; (c)feeding water heated and pressurized to at least supercriticalconditions externally of said reactor to at least one point along saidannular space surrounding said platelet tube reactor, wherein theresulting pressure in said annular space is higher than the pressure inthe center reaction zone within said platelet tube such that saidsupercritical water flows from said annular space through said fluidpassages in the wall of said platelet tube and into said center reactionzone through said plurality of apertures, forming a thin film ofsupercritical water over substantially the entire inner surface of saidplatelet tube and heating said mixture to supercritical reactiontemperature; and (d) reacting said organic waste with said oxidant insaid reaction zone.
 2. The process of claim 1 wherein the temperature ofsaid pressurized aqueous mixture fed to said reaction zone is about 650°F. or less.
 3. The process of claim 2 wherein the said pressurizedaqueous mixture is at about ambient temperature.
 4. The process of claim1 wherein said reaction is conducted at a temperature of from about1100° F. to about 1800° F.
 5. The process of claim 4 wherein saidreaction is conducted at a pressure of from about 4000 to about 6000pounds per square inch.
 6. The process of claim 1 wherein said reactingstep results in reaction products and further comprising:(e) cooling theresulting reaction products to produce a cooled reaction product mixturecomprising gaseous oxidation reaction products, solid inorganicmaterials and water; and (f) after removing gaseous products, separatingand removing said inorganic materials solids from said mixture.
 7. Theprocess of claim 6 further comprising injecting pressurized subcriticalwater into the reaction zone at or near the end thereof to quench thereaction products.
 8. The process of claim 6 further comprising:(g)recycling a portion of said cooled reaction product mixture to step (e).9. The process of claim 1 wherein said supercritical water is fed tosaid reactor at one point along said reaction zone.
 10. The process ofclaim 1 wherein said supercritical water is fed to said reactor atmultiple points along said reaction zone.
 11. The process of claim 1further comprising feeding additional oxidant to said reaction zonetogether with said supercritical water.
 12. The process of claim 1further comprising feeding a supplemental fuel to said reactor as partof said pressurized aqueous mixture.
 13. The process of claim 1 whereineach of said plurality of apertures is shaped so as to direct the flowof supercritical water along said inner surface of said platelet tube.14. The process of claim 1 wherein said plurality of apertures areshaped so as to simultaneously direct the flow of supercritical watersubstantially perpendicularly from said inner surface of said platelettube into said pressurized aqueous mixture in said reaction zone, andalong said inner surface of said platelet tube.
 15. A process for thesupercritical water oxidation of an organic waste materialcomprising:(a) feeding a pressurized aqueous mixture containing saidwaste material and an oxidant source at ambient temperature to a centerreaction zone of a platelet tube reactor which is supported within anouter shell and whose outer surface defines, together with an innersurface of said shell, an annular space, a wall of said platelet tubebeing provided with fluid passages which permit the flow of fluid fromsaid annular space into said center reaction zone through a plurality ofapertures; (b) igniting a fuel at an inlet of said reaction zone toincrease the temperature of said pressurized aqueous mixture; (c)feeding water heated and pressurized to at least supercriticalconditions externally of said reactor to multiple locations along saidannular space surrounding said platelet tube reactor, wherein theresulting pressure in said annular space is higher than the pressure inthe center reaction zone within said platelet tube such that saidsupercritical water flows from said annular space through said fluidpassages in the wall of said platelet tube and into said center reactionzone through said plurality of apertures, forming a thin film ofsupercritical water over substantially the entire inner surface of saidplatelet tube and heating said mixture to supercritical reactiontemperature; and (d) reacting said organic waste with said oxidant insaid reaction zone at a temperature of from about 1100° F. to about1800° F. to produce a reaction product mixture containing gaseousoxidation reaction products, insoluble solid inorganic material andwater; and (e) separating and removing said solids from said reactionproduct mixture.
 16. The process of claim 15 wherein said separatingstep (e) includes subjecting said reaction product mixture to avapor/solid separation step.
 17. The process of claim 15 wherein saidseparating step (e) comprises cooling said reaction product mixture,removing gaseous products therefrom and then separating solids from theresulting mixture.
 18. The process of claim 17 further comprisingrecycling a portion of said cooled reaction product mixture to said step(e) and subjecting the remaining portion of said cooled reaction productmixture to said solids separation step.
 19. The process of claim 15wherein each of said plurality of apertures is shaped so as to directthe flow of supercritical water along said inner surface of saidplatelet tube.
 20. The process of claim 15 wherein said plurality ofapertures are shaped so as to simultaneously direct the flow ofsupercritical water substantially perpendicularly from said innersurface of said platelet tube into said pressurized aqueous mixture insaid reaction zone, and along said inner surface of said platelet tube.21. A process for the oxidation of an organic waste materialcomprising:(a) feeding a pressurized aqueous mixture of water and saidwaste material to a center zone of a platelet tube reactor which issupported within an outer shell and whose outer surface defines,together with an inner surface of said shell, an annular space, a wallof said platelet tube being provided with fluid passages which permitthe flow of fluid from said annular space into said center zone througha plurality of apertures; (b) igniting a fuel at an inlet of saidreaction zone to increase the temperature of said pressurized aqueousmixture; (c) feeding water heated and pressurized to at leastsupercritical conditions externally of said reactor to at least onepoint along said annular space surrounding said platelet tube reactor,wherein the resulting pressure in said annular space is higher than thepressure in the center zone within said platelet tube such that saidsupercritical water flows from said annular space through said fluidpassages in the wall of said platelet tube and into said center zonethrough said plurality of apertures, forming a thin film ofsupercritical water over substantially the entire inner surface of saidplatelet tube and heating said mixture to supercritical temperature; (d)separating organic components from inorganic components of said wastematerial while at supercritical conditions; and (e) oxidizing saidseparated organic components outside of said platelet tube reactor. 22.The process of claim 21 wherein said separating step (d) includesseparating a reaction product mixture and further comprising subjectingsaid reaction product mixture to a vapor/solid separation step.
 23. Theprocess of claim 21 wherein said separating step (d) includes separatinga reaction product mixture and further comprising cooling said reactionproduct mixture, removing gaseous products therefrom and then separatingsolids from the resulting mixture.
 24. The process of claim 23 furthercomprising recycling a portion of said cooled reaction product mixtureto said step (d) and subjecting the remaining portion of said cooledreaction product mixture to said solids separation step.
 25. The processof claim 21 wherein each of said plurality of apertures is shaped so asto direct the flow of supercritical water along said inner surface ofsaid platelet tube.
 26. The process of claim 21 wherein said pluralityof apertures are shaped so as to simultaneously direct the flow ofsupercritical water substantially perpendicularly from said innersurface of said platelet tube into said pressurized aqueous mixture insaid reaction zone, and along said inner surface of said platelet tube.